The present invention relates to a tone synthesizing device and method based on a physical model tone generator simulating or modelling the tone generating mechanism of natural musical instruments, and a recording medium storing a tone synthesizing program. More particularly, the present invention relates to a tone synthesizing device designed to model the tone generating mechanism of rubbed string instruments such as a violin.
Physical model tone generators have been known which are designed to model the tone generating mechanism of natural musical instruments to thereby synthesize tones of the natural musical instruments or tone signals of an unreal musical instrument. In such a physical model tone generator modelling a rubbed string instrument, pitch information and performance information, such as a bowing pressure and bowing velocity, is manually input by use of a keyboard, pointing device, such as a mouse, and other necessary operator. Parameters to be used in the physical model tone generator are varied in response to the input information, to synthesize time-varying tone signals of a tone color or timbre similar to or exceeding that of the modelled natural musical instrument.
FIGS. 13A and 13B are block diagrams showing a conventional tone synthesizing device modelling a rubbed string instrument; more specifically, FIG. 13A shows a general organization of the tone synthesizing device while FIG. 13B shows an inner construction of a nonlinear section 133 in the tone synthesizing device. In these figures, reference numerals 10, 14 and 16 represent adders, 131 and 132 delay filters, 133 the nonlinear section, 134 a divider, 135 a nonlinear function section, and 136 a multiplier.
In FIG. 13A, the adders 10 and 14 correspond to a string-rubbing point of the rubbed string instrument, and the delay filter 131 functions to model propagation characteristics of a vibratory wave produced at the string-rubbing point, reaching the left end of the string and then reflected off the left end to return to the string-rubbing point. Similarly, the other delay filter 132 functions to model propagation characteristics of a vibratory wave created at the string-rubbing point, reaching the right end of the string and then reflected off the right end to return to the string-rubbing point. A closed loop is formed via these delay filters 131 and 132, and the resonant frequency of the string is determined by a delay time in the closed loop. These elements together constitute a linear unit of the tone synthesizing device. The nonlinear section 133 functions to model a frictional drive of the string by the bow. The adder 16 combines together signals corresponding to the vibratory waves propagating in the leftward and rightward directions and provides the resultant combined signal as a loop output signal LOOP. The loop output signal LOOP is modified in accordance with a bowing velocity Vb and bowing pressure Pb as performance parameters, and the thus-modified loop output signal LOOP is sent back to the linear unit via the adders 10 and 14.
Within the nonlinear section 133, as shown in FIG. 13B, the loop output signal LOOP supplied from the linear unit is given to an adder 5, where the bowing velocity Vb is subtracted from the loop output signal LOOP. After the subtraction, the loop output signal LOOP is divided by the bowing pressure Pb by means of the divider 134 and then passed to the nonlinear function section 135. Output from the nonlinear function section 135 is multiplied by the bowing pressure Pb by means of the multiplier 136.
FIG. 14 is a graph explanatory of an input-output characteristic of the nonlinear function section 135 shown in FIGS. 13A and 13B. In FIG. 14, the horizontal axis represents the input to the divider 134, i.e., a relative velocity between the loop output signal LOOP from the linear unit and the bowing velocity Vb (LOOP-Vb), while the vertical axis represents the output from the multiplier 136. The basic characteristics are determined by the nonlinear function section 135. Predetermined input range B, centering around the zero input level in FIG. 14, represents a situation where a driving force corresponding to a movement of the bow is being given to the string by a frictional engagement between the bow and the string. Thus, in this situation, the string presents a motion governed by a stationary friction coefficient.
However, when the bow is moved at a velocity within another input range A beyond the predetermined input range B, a slip would occur between the bow and the string, so that the string movement would be governed by a dynamic frictional coefficient smaller than the stationary friction coefficient and thus the driving force applied from the bow to the string would drop abruptly. As a consequence, the string would move back toward a free or undriven condition from the driven condition where it is being displaced in accordance with the movement of the bow. Therefore, a time interval between points at which the input range B causing the string to move with the stationary friction coefficient shifts to the input range A causing the string to move with the dynamic friction coefficient would have some connection to the period of the driving force that brings about vibration of the string. The boundary point between the input range B and the input range A would vary depending on the bowing pressure Pb. Namely, the greater the bowing pressure Pb, the greater becomes the relative velocity causing the slip between the bow and the string. The divider 134 and multiplier 136 cooperate with each other for modelling such a variation of the boundary point (characteristic changing point) responding to a variation of the bowing pressure Pb.
Further, with the rubbed string instruments typified by a violin, there would be generated an unintended "out-of-tune" tone through a certain bowing pressure or finger motion applied by a human player during the course of a bowing operation. This "out-of-tune" tone corresponds to a "falsetto" of a human singer and can be described as a physical phenomenon where the string vibration shifts from a fundamental vibration mode to a second-order (second harmonic) or higher-order vibration mode. Therefore, to keep generating tones of desired pitches in a stable manner requires a considerable performance skill on the part of a human player, due to dynamic variations in the frictional relationship, such as the above-mentioned slip, between the bow and the string.
The above-noted phenomenon would occur, for example, where the desired stationary frictional relationship, involving no slip between the string and the bow, frequently shifts to the dynamic frictional relationship due to occurrence of the slip. With the physical model tone generator modelling the tone generating mechanism of the rubbed string instrument as well, there could, in theory, occur a similar phenomenon of the fundamental vibration mode shifting to a higher-order vibration mode, particularly, depending on the parameter settings. In the illustrated example of FIG. 14, this phenomenon corresponds to such a condition where the period, in which the input range B where the string is caused to move with the stationary friction coefficient shifts to the input range A where the string is caused to move with the dynamic friction coefficient, becomes shorter than the fundamental pitch period.
In the violin, the bow is made of a bundle of horse's tail hair, and tones are generated with relatively rough fluctuations due to fine unevenness in the surfaces of the bow and the string. Thus, to faithfully approximate the tone color of the rubbed string instrument, it is necessary to impart the fluctuations to the tones. Tone synthesizing device capable of imparting such fluctuations is known from, for example, Japanese Patent Laid-open Publication No. HEI-4-306698, where tone parameters representing a bowing pressure are varied in accordance with random number signals. However, because the known tone synthesizing device is not designed to control the fluctuations in accordance with the string's vibrating movement and the like, it can not fully model the tonal fluctuations resulting from the surface conditions of the bow etc.